U.S. patent number 11,161,943 [Application Number 16/627,661] was granted by the patent office on 2021-11-02 for production method for poly(vinyl alcohol).
This patent grant is currently assigned to Denka Company Limited. The grantee listed for this patent is DENKA COMPANY LIMITED. Invention is credited to Takayuki Oshima, Shin Sugimura.
United States Patent |
11,161,943 |
Sugimura , et al. |
November 2, 2021 |
Production method for poly(vinyl alcohol)
Abstract
Disclosed is a production method for a poly(vinyl alcohol)
having a degree of saponification of 97.0 mol % or more,
comprising: a pulverization step of pulverizing a first poly(vinyl
alcohol) having a particulate form to obtain a second poly(vinyl
alcohol) having an adjusted particle size, and a heating step of
heating the second poly(vinyl alcohol).
Inventors: |
Sugimura; Shin (Itoigawa,
JP), Oshima; Takayuki (Itoigawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
DENKA COMPANY LIMITED |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Denka Company Limited (Toyko,
JP)
|
Family
ID: |
1000005907140 |
Appl.
No.: |
16/627,661 |
Filed: |
July 10, 2017 |
PCT
Filed: |
July 10, 2017 |
PCT No.: |
PCT/JP2017/025142 |
371(c)(1),(2),(4) Date: |
December 30, 2019 |
PCT
Pub. No.: |
WO2019/012581 |
PCT
Pub. Date: |
January 17, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200157289 A1 |
May 21, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J
3/12 (20130101); C08J 2329/04 (20130101) |
Current International
Class: |
C08J
3/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
55099925 |
|
Jul 1980 |
|
JP |
|
S61-046241 |
|
Mar 1986 |
|
JP |
|
H2-225506 |
|
Sep 1990 |
|
JP |
|
05339380 |
|
Dec 1993 |
|
JP |
|
H5-339380 |
|
Dec 1993 |
|
JP |
|
H8-301936 |
|
Nov 1996 |
|
JP |
|
H9-302024 |
|
Nov 1997 |
|
JP |
|
2003-055889 |
|
Feb 2003 |
|
JP |
|
2004-315345 |
|
Nov 2004 |
|
JP |
|
2006-028233 |
|
Feb 2006 |
|
JP |
|
2015-025211 |
|
Feb 2015 |
|
JP |
|
Other References
Japan Patent Office, International Search Report in International
Application No. PCT/2017/025142 (dated Sep. 5, 2017). cited by
applicant .
Japan Patent Office, Written Opinion in International Application
No. PCT/2017/025142 (dated Sep. 5, 2017). cited by applicant .
International Bureau of WIPO, International Preliminary Report on
Patentability in International Application No. PCT/2017/025142
(dated Jan. 14, 2020). cited by applicant .
European Patent Office, Extended European Search Report in European
Patent Application No. 17917781.1 (dated Mar. 17, 2020). cited by
applicant.
|
Primary Examiner: Kaucher; Mark S
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
The invention claimed is:
1. A production method for a poly(vinyl alcohol) having a degree of
saponification of 97.0 mol % or more, the method comprising: a
pulverization step of pulverizing a first poly(vinyl alcohol)
having a particulate form to obtain a second poly(vinyl alcohol)
having an adjusted particle size; and a heating step of heating the
second poly(vinyl alcohol), wherein the second poly(vinyl alcohol)
is heated after at least one of an alcohol and water is adhered to
a surface of the second poly(vinyl alcohol); wherein, in the
pulverization step, the first poly(vinyl alcohol) is pulverized
such that a proportion of a poly(vinyl alcohol) having a particle
diameter of 53 .mu.m or less in the second poly(vinyl alcohol) is
50 mass % or less and a proportion of a poly(vinyl alcohol) having
a particle diameter of 180 .mu.m or more in the second poly(vinyl
alcohol) is 5 mass % or less.
2. The production method according to claim 1, wherein, in the
heating step, the second poly(vinyl alcohol) is heated after an
alcohol and water are adhered to a surface of the second poly(vinyl
alcohol).
3. The production method according to claim 1, wherein the
poly(vinyl alcohol) having a degree of saponification of 97.0 mol %
or more has a solubility in cold water of 10.0% or less and a
degree of swelling of 5.0 or less.
4. The production method according to claim 1, wherein the
poly(vinyl alcohol) having a degree of saponification of 97.0 mol %
or more is utilized as a binder for glass paper.
5. The production method according to claim 1, wherein a heating
temperature in the heating step is 80.degree. C. or more.
6. The production method according to claim 5, wherein the heating
temperature in the heating step is 180.degree. C. or less.
Description
CROSS-REFERENCE TO A RELATED APPLICATION
This patent application is the U.S. national phase of International
Application No. PCT/JP2017/025142, filed on Jul. 10, 2017, the
disclosure of which is incorporated herein by reference in its
entirety for all purposes.
TECHNICAL FIELD
The present invention relates to a production method for a
poly(vinyl alcohol).
BACKGROUND ART
In recent years, the use of inorganic fiber paper or chemical
synthetic fiber paper, which is a type of nonwoven fabric produced
from chemical synthetic fibers or inorganic fibers by a paper
making method, has increased in various fields. Examples of the
inorganic fiber paper include glass paper which is a nonwoven
fabric made from glass fiber. Glass paper is generally produced by
a method including a paper making step of spreading a slurry
containing glass fibers and a particulate poly(vinyl alcohol)
(hereinafter, also simply referred to as "poly(vinyl alcohol)") as
an internal binder into a sheet form. In the case where a glass
paper is produced by this method, a poly(vinyl alcohol) having a
high degree of saponification is used. In addition, in order to
maintain the strength and the surface smoothness of the glass
paper, the particle size, the solubility in cold water, the degree
of swelling, etc. of the poly(vinyl alcohol) need to be adjusted to
a desired range.
A particulate poly(vinyl alcohol) is productized by separating a
mother liquid from a solution containing a poly(vinyl alcohol)
obtained by polymerization of a vinyl ester such as vinyl acetate
and saponification of the polyvinyl ester, drying the poly(vinyl
alcohol), and then pulverizing the dried poly(vinyl alcohol) (for
example, Patent Literature 1).
CITATION LIST
Patent Literature
Patent Literature 1: Japanese Unexamined Patent Publication No.
2006-28233
SUMMARY OF INVENTION
Technical Problem
In the conventional production method, however, adjustment to a
desired particle size of poly(vinyl alcohol) by pulverizing results
in significant increase in the solubility in cold water and the
degree of swelling, so that it is difficult to obtain a poly(vinyl
alcohol) (suitable for use in glass paper or the like) satisfying
all of the particle size, the solubility in cold water and the
degree of swelling in parallel.
An object of the present invention is, therefore, to provide a
production method for a poly(vinyl alcohol) enabling all of the
particle size, the solubility in cold water and the degree of
swelling to be adjusted to a desired range.
Solution to Problem
The production method for a poly(vinyl alcohol) of the present
invention is a production method for a poly(vinyl alcohol) having a
degree of saponification of 97.0 mol % or more, comprising a
pulverization step of pulverizing a first poly(vinyl alcohol)
having a particulate form to obtain a second poly(vinyl alcohol)
having an adjusted particle size, and a heating step of heating the
second poly(vinyl alcohol).
According to the production method, all of the particle size, the
solubility in cold water, and the degree of swelling of a
poly(vinyl alcohol) can be adjusted to a desired range.
Specifically, in the production method, the particle size of a
poly(vinyl alcohol) is adjusted to a desired range in a
pulverization step, and the solubility in cold water and the degree
of swelling of the poly(vinyl alcohol) increased by the
pulverization step can be reduced in a heating step for adjustment
to a desired range.
The heating step may be a step in which the second poly(vinyl
alcohol) is heated after at least one of an alcohol and water is
adhered to a surface of the second poly(vinyl alcohol). Adhering an
alcohol or water to the surface of the second poly(vinyl alcohol)
enables the solubility in cold water and the degree of swelling to
be adjusted in a shorter time.
The heating step may be a step in which the second poly(vinyl
alcohol) is heated after an alcohol and water are adhered to a
surface of the second poly(vinyl alcohol). Adhering an alcohol and
water to the surface of the second poly(vinyl alcohol) enables the
solubility in cold water and the degree of swelling to be adjusted
in a shorter time.
The pulverization step may be a step in which the first poly(vinyl
alcohol) is pulverized such that a proportion of a poly(vinyl
alcohol) having a particle diameter of 53 .mu.m or less in the
second poly(vinyl alcohol) is 50 mass % or less, and that a
proportion of a poly(vinyl alcohol) having a particle diameter of
180 .mu.m or more in the second poly(vinyl alcohol) is 5 mass % or
less. Through adjustment of the particle size of the second
poly(vinyl alcohol) in such a manner in the pulverization step, for
example, a poly(vinyl alcohol) useful as a binder to obtain
products such as a glass paper excellent in the strength and the
surface smoothness can be produced.
The poly(vinyl alcohol) having a degree of saponification of 97.0
mol % or more may have a solubility in cold water of 10.0% or less
and a degree of swelling of 5.0 or less.
The poly(vinyl alcohol) having a degree of saponification of 97.0
mol % or more may be used as a binder for glass paper.
Advantageous Effects of Invention
According to the present invention, a production method for a
poly(vinyl alcohol) can be provided, enabling all of the particle
size, the solubility in cold water and the degree of swelling to be
adjusted to a desired range.
DESCRIPTION OF EMBODIMENTS
Embodiments of the present invention are described in detail as
follows. The present invention is not limited to the following
embodiments.
A production method for a poly(vinyl alcohol) of the present
embodiment comprises a pulverization step of pulverizing a first
poly(vinyl alcohol) having a particulate form to obtain a second
poly(vinyl alcohol) having an adjusted particle size, and a heating
step of heating the second poly(vinyl alcohol).
The pulverization step is a step of pulverizing a first poly(vinyl
alcohol) having a particulate form to obtain a second poly(vinyl
alcohol) having an adjusted particle size.
The first poly(vinyl alcohol) may be prepared by saponifying all or
part of a polyvinyl ester obtained by polymerization of a vinyl
ester, or may be a commercially available poly(vinyl alcohol).
The polyvinyl ester may be a homopolymer of a vinyl ester, or a
copolymer of a vinyl ester and a monomer other than a vinyl ester,
copolymerizable with the vinyl ester, and in view of stability of
the first poly(vinyl alcohol), a homopolymer of a vinyl ester is
preferred.
The vinyl ester may be, for example, vinyl acetate, vinyl
propionate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl
laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, etc., and
in view of easiness of polymerization, vinyl acetate is
preferred.
The monomer other than a vinyl ester, copolymerizable with a vinyl
ester may be, for example, .alpha.-olefin monomers such as ethylene
and propylene; alkyl (meth)acrylate ester monomers such as methyl
(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate and
2-ethylhexyl (meth)acrylate; unsaturated amide monomers such as
(meth)acrylamide and N-methylol acrylamide; unsaturated carboxylic
acid monomers such as (meth)acrylic acid, crotonic acid, maleic
acid, itaconic acid and fumaric acid; alkyl (methyl, ethyl, propyl,
etc.) ester monomers of unsaturated carboxylic acids; anhydrides of
unsaturated carboxylic acids such as maleic anhydride; salts of
unsaturated carboxylic acids with sodium, potassium, ammonium,
etc.; glycidyl group-containing monomers such as allyl glycidyl
ether and glycidyl (meth)acrylate; sulfonic acid group-containing
monomers such as 2-acrylamide-2-methylpropane sulfonic acid or
salts thereof; phosphate group-containing monomers such as acid
phosphooxyethyl methacrylate and acid phosphooxypropyl
methacrylate; and alkyl vinyl ether monomers.
In polymerization of vinyl esters, a polymerization initiator may
be used. The polymerization initiator may be, for example, a
radical polymerization initiator. The radical polymerization
initiator may be azo compounds such as azobisisobutyronitrile and
azobisdimethylvaleronitrile, organic peroxides such as benzoyl
peroxide and dicumyl peroxide, inorganic peroxides such as
potassium persulfate, and redox polymerization initiators such as
cerium(IV) salt-alcohol.
The polymerization method of vinyl esters may be a known
polymerization method such as a solution polymerization, a
suspension polymerization and a bulk polymerization, and a solution
polymerization is preferred due to easiness of operation. Also, the
polymerization method of vinyl esters is preferably a solution
polymerization in alcohol, because the solvent can be commonly used
for the subsequent saponification reaction. In the case of solution
polymerization, the polymerization reaction temperature is
preferably 30.degree. C. or more and may be 90.degree. C. or
less.
The saponification is performed by dissolving a polyvinyl ester
obtained by polymerization in alcohol to prepare an alcohol
solution for an ester exchange reaction (alcoholysis) between the
ester in the molecule and alcohol in the presence of an alkali
catalyst or an acid catalyst.
Examples of the alcohol as a solvent for the saponification
reaction include methanol, ethanol, propanol and butanol. The
concentration of the polyvinyl ester in the alcohol solution may
be, for example, 10 mass % or more and 80 mass % or less. The
reaction temperature of the saponification may be, for example,
10.degree. C. or more or 30.degree. C. or more, and 70.degree. C.
or less or 40.degree. C. or less. The reaction time of the
saponification may be, for example, 30 minutes or more and 3 hours
or less.
The alkali catalyst may be, for example, hydroxides of an alkali
metal such as sodium hydroxide and potassium hydroxide. The acid
catalyst may be, for example, an aqueous solution of inorganic
acids such as hydrochloric acid and sulfuric acid, or an organic
acid such as p-toluenesulfonic acid. The amount of these catalysts
used may be, for example, 1 mmol equivalent or more and 100 mmol
equivalents or less relative to the polyvinyl ester.
The degree of saponification of the first poly(vinyl alcohol) is,
for example, preferably 97.0 mol % or more, more preferably 97.5
mol % or more, still more preferably 98.0 mol % or more,
furthermore preferably 98.5 mol % or more, particularly preferably
99.0 mol % or more.
Generally, as the degree of saponification increases, the
solubility of poly(vinyl alcohol) in water decreases. In the case
where a poly(vinyl alcohol) is used as a binder for glass paper, it
is preferable that the degree of saponification be set high (for
example, 99.0 mol % or more) to prevent the poly(vinyl alcohol)
from falling down together with water during spreading of glass
fibers into a paper form from slurry in a paper making process.
However, according to the production method of the present
embodiment, the solubility in cold water can be lowered by
adjustment of the solubility in cold water, so that even a
poly(vinyl alcohol) having a relatively low degree of
saponification can be used as the first poly(vinyl alcohol).
The "degree of saponification" herein refers to a value calculated
based on the measurement in accordance with JIS K 6726 "3.5 Degree
of saponification."
The degree of saponification may be quickly and accurately
calculated using a near infrared analyzer. For example, first, near
infrared absorption spectra of standard samples of a plurality of
poly(vinyl alcohol)s having specified degrees of saponification are
measured, and a calibration curve is made from the measurement
results through multiple regression analysis, a principal component
regression analysis method, a partial least square method, etc., so
that the degree of saponification of a target poly(vinyl alcohol)
can be measured. According to the measurement method using a near
infrared analyzer, it is also possible to measure the degree of
saponification of a poly(vinyl alcohol) in a production
process.
The method of saponifying a polyvinyl ester may be a conventional
method such as a belt-saponification method and a
kneader-saponification method, and in view of easiness of
production, a belt-saponification method is preferred.
The viscosity average degree of polymerization of the first
poly(vinyl alcohol) may be 100 or more, 700 or more, or 1000 or
more, and may be 10000 or less, 6000 or less, or 4000 or less.
The "viscosity average degree of polymerization" herein is
calculated from the intrinsic viscosity [.eta.] (g/dL) measured at
30.degree. C. with an Ostwald viscometer using ion exchange water
as a solvent, based on the following formula (1).
log(P)=1.613.times.log([.eta.].times.10.sup.4/8.29) (1) Here, P
represents the viscosity average degree of polymerization.
The first poly(vinyl alcohol) may contain a poly(vinyl alcohol)
having a large particle diameter. The proportion of a poly(vinyl
alcohol) having a particle diameter of 180 .mu.m or more in the
first poly(vinyl alcohol) may be 5 mass % or more, 10 mass % or
more, 20 mass % or more, or 50 mass % or more. The proportion of a
poly(vinyl alcohol) having a particle diameter of 53 .mu.m or less
in the first poly(vinyl alcohol) may be 5 mass % or less, or may be
0 mass % (containing no poly(vinyl alcohol) having a particle
diameter of 53 .mu.m or less).
Herein, the proportion of a poly(vinyl alcohol) having a particle
diameter of 180 .mu.m or more refers to the proportion of a
poly(vinyl alcohol) remaining on a sieve (product on sieve) on mass
basis, when a poly(vinyl alcohol) as a measurement target (for
example, the first poly(vinyl alcohol)) is sieved with a test sieve
(nominal opening: 180 .mu.m) described in JIS Z 8801-1: 2006, i.e.,
(mass of product on sieve/total mass of poly(vinyl alcohol) as
measurement target). Herein, the proportion of a poly(vinyl
alcohol) having a particle diameter of 53 .mu.m or less refers to
the proportion of a poly(vinyl alcohol) falling through a sieve
(product under sieve) on mass basis, when a poly(vinyl alcohol) as
a measurement target (for example, the first poly(vinyl alcohol))
is sieved with a test sieve (nominal opening: 53 .mu.m) described
in JIS Z 8801-1: 2006, i.e., (mass of product under sieve/total
mass of poly(vinyl alcohol) as measurement target).
The solubility of the first poly(vinyl alcohol) in cold water may
be 2.0% or more, 3.0% or more, 5.0% or more, or 10.0% or more.
The "solubility in cold water" herein refers to the solubility in
water at 20.0.degree. C. More specifically, 10.0 g (dry mass) of a
poly(vinyl alcohol) is added to 240.0 g of pure water at
20.0.degree. C. and stirred for 15 minutes, and the mixture is then
left standing still for 60 minutes to collect the supernatant with
a 10-mL pipette, which is dried at 150.degree. C. for 45 minutes
for measurement of the solid content of the supernatant to
calculate the concentration of the aqueous solution. The proportion
of the mass of poly(vinyl alcohol) dissolved in water, which is
converted from the concentration of the aqueous solution, to the
dry mass of the initial poly(vinyl alcohol) is taken as the
solubility in cold water. [Solubility in cold water](%)=[mass of
dissolved poly(vinyl alcohol)]/[dry mass of initial poly(vinyl
alcohol)].times.100
The degree of swelling of the first poly(vinyl alcohol) may be 10.0
or less, 5.0 or less, or less than 2.0.
The "degree of swelling" herein is obtained as follows. To 240.0 g
of pure water at 20.0.degree. C., 10.0 g (dry mass) of a poly(vinyl
alcohol) is added and stirred for 15 minutes, and then stirring is
stopped to leave the mixture standing still for 60 minutes. Then,
the mass of poly(vinyl alcohol) in a swollen state collected by
filtration with a Buchner funnel equipped with No. 5A filter paper
is measured. The ratio of the mass to the dry mass of initial
poly(vinyl alcohol) is taken as the degree of swelling. [Degree of
swelling]=[mass of poly(vinyl alcohol) in wet state collected by
filtration]/[dry mass of initial poly(vinyl alcohol)]
Examples of the pulverization method for pulverizing the first
poly(vinyl alcohol) include a wet method in which poly(vinyl
alcohol) in a slurry state containing a mother liquid for
saponification is pulverized and a dry method in which after
removal of the mother liquid from the slurry, the resulting
poly(vinyl alcohol) is pulverized and dried. Since the particle
size of the first poly(vinyl alcohol) can be more easily
controlled, the pulverization step is preferably a step of
pulverizing the first poly(vinyl alcohol) having a particulate form
by a dry method to obtain the second poly(vinyl alcohol) having an
adjusted particle size.
As a pulverizer, known pulverizers can be used, and examples
thereof include ACM Pulverizer and Fine Impact Mill manufactured by
Hosokawa Micron Corporation, Free Pulverizer manufactured by Nara
Machinery Co., Ltd., Turbo Mill and Turbo Disk Mill manufactured by
Freund-Turbo Corporation, and HID series manufactured by Orenda
Pulverizers Inc.
In the pulverization step, the first poly(vinyl alcohol) may be
pulverized such that the proportion of poly(vinyl alcohol) having a
particle diameter of 53 .mu.m or less in the second poly(vinyl
alcohol) is 50 mass % or less and that the proportion of poly(vinyl
alcohol) having a particle diameter of 180 .mu.m or more in the
second poly(vinyl alcohol) is 5 mass % or less.
The proportion of poly(vinyl alcohol) having a particle diameter of
53 .mu.m or less in the second poly(vinyl alcohol) is more
preferably 30 mass % or less, still more preferably 28 mass % or
less, furthermore preferably 20 mass % or less, particularly
preferably 10 mass % or less. The proportion of poly(vinyl alcohol)
having a particle diameter of 180 .mu.m or more in the second
poly(vinyl alcohol) is more preferably 3 mass % or less, still more
preferably 2 mass % or less, particularly preferably 1 mass % or
less.
The particle size of the second poly(vinyl alcohol) can be
adjusted, for example, by pulverizing part or all of the first
poly(vinyl alcohol). In the case where part of the first poly(vinyl
alcohol) is pulverized, for example, the first poly(vinyl alcohol)
may be sieved to fractionate a poly(vinyl alcohol) having a
particle diameter of 180 .mu.m or more, and then the fractionated
poly(vinyl alcohol) having a particle diameter of 180 .mu.m or more
may be pulverized to adjust the particle size of the second
poly(vinyl alcohol). In the case where the proportion of the
poly(vinyl alcohol) having a particle diameter of 53 .mu.m or less
is large, the first poly(vinyl alcohol) may be sieved to
fractionate poly(vinyl alcohol) having a particle diameter of 53
.mu.m or less, and then part or all of the fractionated poly(vinyl
alcohol) having a particle diameter of 53 .mu.m or less may be
removed to adjust the particle size of the second poly(vinyl
alcohol).
The volatile content of the first poly(vinyl alcohol) is, for
example, preferably 5.0 mass % or less, more preferably 4.0 mass %
or less, still more preferably 3.0 mass % or less, based on the
total mass of the first poly(vinyl alcohol). Here, the "volatile
content" refers to a volatile content measured and calculated
according to the description in "3.4 Volatile content" in JIS K
6726-1994, including, for example, solvent components such as
methanol used in the production of the first poly(vinyl alcohol).
Through adjustment of the volatile content to the range described
above, the pulverization step can be more safely performed.
The volatile content may be adjusted by drying the first poly(vinyl
alcohol). In other words, the production method for a poly(vinyl
alcohol) of the present embodiment may further comprise a drying
step of drying the first poly(vinyl alcohol) before the
pulverization step, and the volatile content of the first
poly(vinyl alcohol) may be adjusted to the range described above in
the drying step.
The drying method in the drying step may be natural drying or
forced drying using a drying facility, and a forced drying method
using a drying facility is preferred. It is preferable that the
drying temperature be lower than the temperature at which the first
poly(vinyl alcohol) is thermally damaged. The drying temperature is
preferably 180.degree. C. or less, more preferably 150.degree. C.
or less, still more preferably 120.degree. C. or less. The drying
temperature is, for example, preferably 70.degree. C. or more, more
preferably 80.degree. C. or more, still more preferably 90.degree.
C. or more. The drying time is appropriately selected according to
the drying temperature and the like.
A heating step is a step of heating the second poly(vinyl
alcohol).
The heating temperature in the heating step may be adjusted to
obtain an intended solubility in cold water and an intended degree
of swelling of the poly(vinyl alcohol). In view of preventing
thermal deterioration of the second poly(vinyl alcohol), the upper
limit of the heating temperature is preferably 180.degree. C. or
less, more preferably 150.degree. C. or less, still more preferably
120.degree. C. or less. In view of controlling the solubility in
cold water and the degree of swelling, and of reducing the heating
time, the lower limit of the heating temperature is preferably
70.degree. C. or more, more preferably 80.degree. C. or more, still
more preferably 90.degree. C. or more. The heating temperature can
be adjusted within the range, and may be, for example, 70 to
180.degree. C., 80 to 150.degree. C., or 90 to 120.degree. C. The
heating time is appropriately selected according to the heating
temperature and the like.
It is preferable that the heating step be a step of heating the
second poly(vinyl alcohol) after adhering at least one of an
alcohol and water to the surface of the second poly(vinyl alcohol).
Heating after adherence of the alcohol or water to the surface of
the second poly(vinyl alcohol) enables control of the solubility in
cold water and the degree of swelling to be more efficiently
achieved. It is considered that the adherence of the alcohol or
water causes the second poly(vinyl alcohol) to be partially
dissolved, resulting in easy occurrence of changes in degree of
crystallinity and the like by heating. The heating step is
preferably, for example, a step of heating the second poly(vinyl
alcohol) after adhering at least one of the alcohol and water to
the surface of the second poly(vinyl alcohol), and is more
preferably a step of heating the second poly(vinyl alcohol) after
adhering the alcohol and water to the surface of the second
poly(vinyl alcohol).
The method for adhering at least one of alcohol and water to the
surface of the second poly(vinyl alcohol) may be a method such as
spraying, coating and dipping, and an adhesion method by spraying
is preferred due to easy control of the amount of at least one of
alcohol and water adhered to the second poly(vinyl alcohol) and
easy operation.
In the case where alcohol is adhered to the second poly(vinyl
alcohol), it is preferable that the heating step be performed under
an atmosphere of inert gas such as nitrogen in view of safety.
The alcohol is preferably an alcohol having solubility in water
such as methanol, ethanol, propyl alcohol, butanol and ethylene
glycol. Among these alcohols, methanol is preferred in view of
easiness in use, economy, etc.
The amount of at least one of the alcohol and water adhered is
preferably 0.01 mass % or more, more preferably 0.1 mass % or more,
still more preferably 0.5 mass % or more, based on the total mass
of the second poly(vinyl alcohol). The amount of at least one of
alcohol and water adhered is preferably 10 mass % or less, more
preferably 5.0 mass % or less, still more preferably 2.0 mass % or
less, based on the total mass of the second poly(vinyl alcohol).
With the amount adhered controlled to the range, the heating time
can be reduced, and the occurrence of aggregates formed from the
second poly(vinyl alcohol) fused to each other can be further
prevented.
In the heating step, the alcohol and water each may be used alone,
or the alcohol and water may be mixed for use. In view of more
efficient achievement of control of the solubility in cold water
and the degree of swelling, it is preferable that the alcohol and
water be mixed for use. In the case of using water alone, in view
of further preventing the occurrence of aggregates of particles
formed by partial dissolution of the second poly(vinyl alcohol), it
is preferable that a method be devised such that the particles are
disposed not to come in contact with each other and then brought
into contact with water.
In the case where alcohol and water are mixed for use, the content
of water is preferably 1 mass % or more, more preferably 5 mass %
or more, still more preferably 10 mass % or more, based on the
total mass of alcohol and water. In the case where alcohol and
water are mixed for use, the content of water is preferably 50 mass
% or less, more preferably 30 mass % or less, still more preferably
25 mass % or less, based on the total mass of alcohol and
water.
The poly(vinyl alcohol) obtained by the production method in the
present embodiment may have the following properties.
The degree of saponification of the poly(vinyl alcohol) is 97.0 mol
% or more, and may be 97.5 mol % or more, 98.0 mol % or more, 98.5
mol % or more, or 99.0 mol % or more. The degree of saponification
of the poly(vinyl alcohol) can be controlled by adjusting the
degree of saponification of the first poly(vinyl alcohol).
The solubility of the poly(vinyl alcohol) in cold water is
preferably 10.0% or less, more preferably 9.0% or less, still more
preferably 8.0% or less. The solubility of the poly(vinyl alcohol)
in cold water may be 0.0% or more, 0.5% or more, or 1.0% or more.
With a solubility of the poly(vinyl alcohol) in cold water in the
range, when a slurry mixed with fibers such as inorganic fibers and
chemical synthetic fibers is prepared and the fibers are spread
into a sheet form in a paper making process, the poly(vinyl
alcohol) can be prevented from falling down together with water,
resulting in more sufficient strength of a product to be obtained,
which is preferable. The solubility in cold water can be adjusted
by controlling the degree of pulverization in the pulverization
step and the heating temperature and heating time in the heating
step.
The degree of swelling of the poly(vinyl alcohol) is preferably 5.0
or less, more preferably 4.0 or less, still more preferably 3.4 or
less. The degree of swelling of the poly(vinyl alcohol) is
preferably 2.0 or more, more preferably 2.5 or more, still more
preferably 2.7 or more. The degree of swelling of the poly(vinyl
alcohol) can be adjusted in the range, and may be, for example, 2.0
to 5.0, 2.5 to 5.0, 2.7 to 5.0, or 2.7 to 3.4. With the upper limit
of the degree of swelling of the poly(vinyl alcohol) controlled to
the range, a moderate space can be secured when fibers such as
inorganic fibers and chemical synthetic fibers are fastened to each
other, so that more excellent air permeability of a product is
achieved. With the lower limit of the degree of swelling of the
poly(vinyl alcohol) controlled to the range, fibers such as
inorganic fibers and chemical synthetic fibers can be more
sufficiently fastened to each other, so that the strength of a
resulting product can be further improved. The degree of swelling
can be adjusted by controlling the degree of pulverization in the
pulverization step and the heating temperature and heating time in
the heating step.
The proportion of particles having a particle diameter of 53 .mu.m
or less in the poly(vinyl alcohol) is preferably 50% or less, more
preferably 40% or less, still more preferably 35% or less. The
proportion of particles having a particle diameter of 180 .mu.m or
more in the poly(vinyl alcohol) is preferably 5% or less, more
preferably 3% or less, still more preferably 1% or less. The
particle size of the poly(vinyl alcohol) can be adjusted in the
range, and, for example, the proportion of particles having a
particle diameter of 53 .mu.m or less may be 50% or less and the
proportion of particles having a particle diameter of 180 .mu.m or
more may be 5% or less, the proportion of particles having a
particle diameter of 53 .mu.m or less may be 40% or less and the
proportion of particles having a particle diameter of 180 .mu.m or
more may be 3% or less, or the proportion of particles having a
particle diameter of 53 .mu.m or less may be 35% or less and the
proportion of particles having a particle diameter of 180 .mu.m or
more may be 1% or less.
With the proportion of particles of poly(vinyl alcohol) having a
particle diameter of 53 .mu.m or less controlled to the range, the
poly(vinyl alcohol) can be prevented from falling down together
with water when a slurry mixed with fibers such as inorganic fibers
and chemical synthetic fibers is prepared and framed into a sheet
form, resulting in more sufficient strength of a product to be
obtained. Also, with the proportion of particles of poly(vinyl
alcohol) having a particle diameter of 180 .mu.m or more controlled
to the range in the particle size distribution, the surface state
of a product can be smoother, and the air permeability of a product
can be further improved.
The aspect ratio of the poly(vinyl alcohol) may be, for example,
3.0 or less, 2.0 or less, 1.5 or less, or 1.0. For example, in the
case of using as a binder for glass paper, it is deemed that use of
a poly(vinyl alcohol) having a particulate form having a large
aspect ratio is desired, because use of a poly(vinyl alcohol)
having a small aspect ratio causes the poly(vinyl alcohol) to
easily fall down together with water when glass fibers are spread
into a paper form in a paper making process. The poly(vinyl
alcohol) obtained by the production method of the present
embodiment, however, allows the solubility in cold water and the
degree of swelling to be controlled, so that the poly(vinyl
alcohol) can be sufficiently compounded between glass fibers when
glass fibers are formed into a paper form in a paper making
process.
Herein, the "aspect ratio" refers to a value measured using a
particle size/shape distribution measuring apparatus (manufactured
by Seishin Enterprise Co., Ltd., trade name "PITA-1"), and a value
obtained by dividing the maximum length of an object by the maximum
vertical length. Using methanol as a dispersion medium, the shape
and the number of objects are determined, and the aspect ratio for
the frequency average of the found number can be taken as the
number average aspect ratio. Here, the number of measurements is
set to 2900 to 3100.
According to the production method of the present embodiment, all
of the particle size, the solubility in cold water and the degree
of swelling can be adjusted to a desired range. According to the
present embodiment, therefore, a poly(vinyl alcohol) useful as, for
example, a binder (in particular, internal binder) used for
inorganic fiber paper, chemical synthetic fiber paper, etc., can be
obtained.
Conventionally, products of poly(vinyl alcohol) are produced by
drying a poly(vinyl alcohol) obtained by saponification, and then
pulverizing the dried product. The pulverization of the particles
of poly(vinyl alcohol) for adjustment of the particle size of
poly(vinyl alcohol) results in significant increase in the
solubility in cold water and the degree of swelling, so that it is
difficult to obtain a poly(vinyl alcohol) having desirable physical
properties through adjustment of particle size by pulverization.
Although a means to reduce the solubility in cold water and the
degree of swelling of poly(vinyl alcohol) in advance by
sufficiently drying poly(vinyl alcohol) before pulverization, it is
difficult to reduce as much as the increase in the solubility in
cold water and the degree of swelling caused through
pulverization.
It is considered that the significant increase in the solubility in
cold water and the degree of swelling in water caused by
pulverization of poly(vinyl alcohol) having a particulate form is
caused by the following reason. The poly(vinyl alcohol) having a
particulate form has a high crystalline region at the outer edge of
the particles and a low crystalline region in the internal part of
the particles, and when pulverized, the low crystalline region is
exposed to the surface of the particles. Since the low crystalline
region is more soluble or more swellable in water than the high
crystalline region, it is considered that the solubility in cold
water and the degree of swelling of the poly(vinyl alcohol)
significantly increase after pulverization. On the other hand, in
the production method of the present embodiment, since the degree
of crystallization in the low crystalline region and the like
exposed to the particle surface can be changed by heating the
second poly(vinyl alcohol) after pulverization, it is presumed that
the effect can be obtained.
The poly(vinyl alcohol) obtained by the production method of the
present embodiment can be suitably used for a binder for glass
paper, a binder for insulating board, a binder for inorganic
building panel, etc.
The binder for glass paper containing the poly(vinyl alcohol)
obtained by the production method of the present embodiment is
particularly useful as a so-called internal binder. The "internal
binder" is also referred to as a primary binder, being a component
coexisting with glass fibers in the slurry solution when a glass
paper is made.
The glass paper can be produced on an industrial scale by a wet
internal binder method comprising dispersing glass fibers having a
fiber length of several mm to several tens of mm and a primary
binder in water to prepare a slurry, and spreading the slurry into
a sheet form on a net in a paper making process. Using the
poly(vinyl alcohol) obtained by the production method of the
present embodiment, a glass pager can be used. The glass paper is
obtained, for example, by a production method comprising:
(1) a step of preparing a slurry containing a binder for the glass
paper as a primary binder;
(2) a sheet forming step of preparing a solution containing the
slurry and glass fibers, subjecting the solution to a paper making
process, and removing the solvent to form a sheet; and
(3) a step of letting the resulting sheet pass through a solution
containing a secondary binder and then removing the solvent to
produce a glass paper.
As the secondary binder, the binder for glass paper described above
may be used, or another binder may be used. Examples of another
binder include binders such as poly(vinyl alcohol)s other than ones
described above, styrene-butadiene resins, acrylic resins,
styrene-acrylic resins, vinyl acetate-acrylic resins, and vinyl
acetate-ethylene comonomers.
EXAMPLES
The present invention is specifically described with reference to
Examples as follows. The present invention is not limited to the
following Examples.
<Measurement of Solubility in Cold Water>
The solubility in cold water was measured by the following
method.
To 240.0 g of pure water at 20.0.degree. C., 10.0 g (dry mass) of
poly(vinyl alcohol) to be measured was added and stirred for 15
minutes. The mixture was left standing still for 60 minutes, and a
supernatant was collected with a 10-mL pipette and dried at
150.degree. C. for 45 minutes for measurement of the solid content
of the supernatant to calculate the concentration of aqueous
solution. The proportion of the mass of the poly(vinyl alcohol)
dissolved in water, which was converted from the concentration of
the aqueous solution, to the dry mass of the initial poly(vinyl
alcohol) was taken as the solubility in cold water. [Solubility in
cold water](%)=[mass of poly(vinyl alcohol) dissolved]/[dry mass of
initial poly(vinyl alcohol)].times.100
<Measurement of Degree of Swelling>
The degree of swelling was measured by the following method.
To 240.0 g of pure water at 20.0.degree. C., 10.0 g (dry mass) of a
poly(vinyl alcohol) to be measured was added, stirred for 15
minutes, and then left standing still for 60 minutes. The mass of
the poly(vinyl alcohol) in a wet state collected by filtration with
a Buchner funnel equipped with No. 5A filter paper is then
measured. The ratio of the mass to the dry mass of initial
poly(vinyl alcohol) was taken as the degree of swelling. [Degree of
swelling]=[mass of poly(vinyl alcohol) in wet state collected by
filtration]/[dry mass of initial poly(vinyl alcohol)]
Example 1
In a reaction vessel equipped with a reflux condenser, a dropping
funnel and a stirrer, 100 parts by mass of vinyl acetate, 17.0
parts by mass of methanol, and 0.02 mol % of azobisisobutyronitrile
were placed, and polymerization was performed for 3.0 hours under
the boiling point while stirring under a nitrogen stream.
Subsequently, unreacted vinyl acetate was removed out of the
polymerization system, so that a methanol solution of polyvinyl
acetate having a degree of polymerization of 2175 (solid content
concentration: 30.5 mass %) was obtained.
To the methanol solution of polyvinyl acetate obtained as described
above, a methanol solution of sodium hydroxide (prepared to an
equivalent of 2.5 mmol of sodium hydroxide relative to polyvinyl
acetate) was added to perform a saponification reaction at
40.degree. C. for 60 minutes. After completion of the reaction, a
resulting wet cake was roughly pulverized (apparatus:
explosion-proof transmission mill, pulverization conditions: at a
rotational speed of 4000 rpm for 10 minutes), and the
saponification reaction was stopped by addition of acetic acid.
After removal of the reaction mother liquid by centrifugation, a
first poly(vinyl alcohol) having a particulate form was obtained by
drying in a gear oven at 120.degree. C. for 50 minutes. The
measurements of the degree of saponification, the solubility in
cold water and the degree of swelling of the first poly(vinyl
alcohol) showed that the degree of saponification was 98.1 mol %,
the solubility in cold water was 5.1%, and the degree of swelling
was 1.7. The viscosity average degree of polymerization of the
first poly(vinyl alcohol) was 1700.
The first poly(vinyl alcohol) was sieved using a sieve with an
opening of 180 .mu.m. Using a pulverizer (Mini Speed Mill
manufactured by Labonect K.K.: model number MS-05), the product on
sieve was pulverized (pulverization conditions: at a rotational
speed of 30000 rpm for 3 minutes) and thoroughly mixed with the
product under sieve to prepare a second poly(vinyl alcohol) having
an adjusted particle size. The proportion of particles having a
particle diameter of 53 .mu.m or less in the adjusted second
poly(vinyl alcohol) was 28%, and the proportion of the particles
having a particle diameter of 180 pin or more was 0.2%. The
measurements of the solubility in cold water and the degree of
swelling of the second poly(vinyl alcohol) showed that the
solubility in cold water was 40.2% and the degree of swelling was
5.7.
The second poly(vinyl alcohol) thus obtained was heated in a gear
oven at 130.degree. C. for 4 hours to produce an objective
poly(vinyl alcohol) with a yield of 98%. The measurements of the
degree of saponification, the solubility in cold water and the
degree of swelling of the poly(vinyl alcohol) showed that the
degree of saponification was 98.1 mol %, the solubility in cold
water was 8.8%, and the degree of swelling was 3.3. The results are
shown in Table 1.
Example 2
To 100 parts by mass of the second poly(vinyl alcohol) obtained in
Example 1, 5 parts by mass of methanol was sprayed, and heating was
then performed in a gear oven at 120.degree. C. for 2 hours to
produce an objective poly(vinyl alcohol) with a yield of 98%. The
measurements of the degree of saponification, the solubility in
cold water and the degree of swelling of the poly(vinyl alcohol)
showed that the degree of saponification was 98.1 mol %, the
solubility in cold water was 5.9%, and the degree of swelling was
3.2. The results are shown in Table 1.
Example 3
To 100 parts by mass of the second poly(vinyl alcohol) obtained in
Example 1, 5 parts by mass of a methanol solution containing 5%
water with a mixing ratio of water/methanol of 5/95 was sprayed,
and heating was then performed in a gear oven at 120.degree. C. for
1 hour to produce an objective poly(vinyl alcohol) with a yield of
98%. The measurements of the degree of saponification, the
solubility in cold water and the degree of swelling of the
poly(vinyl alcohol) showed that the degree of saponification was
98.1 mol %, the solubility in cold water was 3.9%, and the degree
of swelling was 2.8. The results are shown in Table 1.
Comparative Example 1
A poly(vinyl alcohol) was obtained in the same manner as in Example
1, except that no heating step was performed. The measurements of
the degree of saponification, the solubility in cold water and the
degree of swelling of the resulting poly(vinyl alcohol) showed that
the degree of saponification was 98.1 mol %, the solubility in cold
water was 40.2%, and the degree of swelling was 5.7. The results
are shown in Table 1.
Comparative Example 2
To a methanol solution of polyvinyl acetate obtained in the same
manner as in Example 1, a methanol solution of sodium hydroxide
(prepared to an equivalent of 2.5 mmol of sodium hydroxide relative
to polyvinyl acetate) was added to perform a saponification
reaction at 40.degree. C. for 60 minutes. After completion of the
reaction, a resulting wet cake was roughly pulverized (apparatus:
explosion-proof transmission mill, pulverization conditions: at a
rotational speed of 4000 rpm for 10 minutes), and the
saponification reaction was stopped by addition of acetic acid.
After removal of the reaction mother liquid by centrifugation, a
first poly(vinyl alcohol) having a particulate form was obtained by
drying in a gear oven at 120.degree. C. for 100 minutes. The
measurements of the degree of saponification, the solubility in
cold water and the degree of swelling of the first poly(vinyl
alcohol) showed that the degree of saponification was 98.2 mol %,
the solubility in cold water was 2.3%, and the degree of swelling
was 1.6. The viscosity average degree of polymerization of the
first poly(vinyl alcohol) was 1700.
The first poly(vinyl alcohol) thus obtained was sieved using a
sieve with an opening of 180 .mu.m. Using a pulverizer (Mini Speed
Mill manufactured by Labonect K.K.: model number MS-05), the
product on sieve was pulverized (pulverization conditions: at a
rotational speed of 30000 rpm for 3 minutes) and thoroughly mixed
with the product under sieve to prepare a poly(vinyl alcohol). The
proportion of particles having a particle diameter of 53 .mu.m or
less in the poly(vinyl alcohol) was 32%, and the proportion of the
particles having a particle diameter of 180 .mu.m or more was 0.4%.
The measurements of the solubility in cold water and the degree of
swelling of the poly(vinyl alcohol) showed that the solubility in
cold water was 28.6% and the degree of swelling was 5.4. The
results are shown in Table 1.
TABLE-US-00001 TABLE 1 Comp. Comp. Exam- Exam- Exam- Exam- Exam-
ple 1 ple 2 ple 3 ple 1 ple 2 First Degree of saponification (mol
%) 98.1 98.1 98.1 98.1 98.2 poly(vinyl Viscosity average degree of
1700 1700 1700 1700 1700 alcohol) polymerization Solubility in cold
water (%) 5.1 5.1 5.1 5.1 2.3 Degree of swelling 1.7 1.7 1.7 1.7
1.6 Second Proportion of particles having a particle 0.2 0.2 0.2
0.2 0.4 poly(vinyl diameter of 180 .mu.m or more (mass %) alcohol)
Proportion of particles having a particle 28 28 28 28 32 diameter
of 53 .mu.m or less (mass %) Solubility in cold water (%) 40.2 40.2
40.2 40.2 28.6 Degree of swelling 5.7 5.7 5.7 5.7 5.4 Condition
Solvent -- Methanol Methanol -- -- for heating containing step 5%
water Amount of solvent sprayed (%) -- 5 5 -- -- Heating
temperature (.degree. C.) 130 120 120 -- -- Heating time (hours) 4
2 1 -- -- Poly(vinyl Degree of saponification (mol %) 98.1 98.1
98.1 98.1 98.2 alcohol) Solubility in cold water (%) 8.8 5.9 3.9 --
-- Degree of swelling 3.3 3.2 2.8 -- --
* * * * *